The parts of blood

Human blood is made of blood cells and a fluid called plasma. Plasma carries red and white blood cells and platelets. Each part of blood has a special function. These parts can be separated from each other. Bone marrow, the soft, spongy material in the center of the bones, makes most of the body’s blood cells. Here is a look at each part of the blood, and why it might be transfused:

Red blood cells. These cells carry oxygen from your lungs to other body organs. They also carry carbon dioxide back to the lungs to be breathed out (exhaled). The body needs a certain number of these cells to work well. Bleeding due to injury, surgery, or disease may cause a low red blood cell count. This is the most common type of transfusion.

White blood cells. These cells fight infections by destroying bacteria, viruses, and other germs. White blood cells are rarely transfused. They are often set aside as a short-term (temporary) treatment for people with a low white cell count and severe infection that has not responded to antibiotics.

Platelets. These tiny cells in your blood help form clots and stop bleeding. Your body may not make enough platelets. This might be from bone marrow disorders, increased destruction of platelets, or medicines such as chemotherapy. Platelets may be transfused before surgery. Or any time the platelet count is very low and you are at risk of bleeding.

Plasma. This fluid carries the blood cells all over the body. It contains proteins, vitamins, and minerals. Some of the proteins also help blood to clot. Plasma or fresh frozen plasma can be transfused in people who severely lack certain parts of the blood that help with clotting.